Stockbroker grapevine (poj 1125 Floyd + enumeration)

Language:DefaultStockbroker grapevine Time limit:1000 ms   Memory limit:10000 K Total submissions:27445   Accepted:15211 Description Stockbrokers are known to overreact to rumours. you have been contracted to develop a method of spreading disinformation amongst the stockbrokers to give your employer the tactical edge in the stock market. for maximum effect, you have to spread the rumours in the fastest possible way. Unfortunately for you, stockbrokers only trust information coming from their "trusted sources" This means you have to take into account the structure of their contacts when starting a rumour. it takes a certain amount of time for a specific stockbroker to pass the rumour on to each of his colleagues. your task will be to write a program that tells you which stockbroker to choose as your starting point for the rumour, as well as the time it will take for the rumour to spread throughout the stockbroker community. this duration is measured as the time needed for the last person to receive the information. Input Your program will input data for different sets of stockbrokers. each set starts with a line with the number of stockbrokers. following this is a line for each stockbroker which contains the number of people who they have contact with, who these people are, and the time taken for them to pass the message to each person. the format of each stockbroker line is as follows: The line starts with the number of contacts (N), followed by N pairs of integers, one pair for each contact. each pair lists first a number referring to the contact (e.g. A '1' means person number one in the set), followed by the time in minutes taken to pass a message to that person. there are no special punctuation symbols or spacing rules. Each person is numbered 1 through to the number of stockbrokers. the time taken to pass the message on will be between 1 and 10 minutes (random SIVE), and the number of contacts will range between 0 and one less than the number of stockbrokers. the number of stockbrokers will range from 1 to 100. the input is terminated by a set of stockbrokers containing 0 (zero) people. Output For each set of data, your program must output a single line containing the person who results in the fastest message transmission, and how long before the last person will receive any given message after you give it to this person, measured in integer minutes. It is possible that your program will receive a network of connections that excludes some persons, I. e. some people may be unreachable. if your program detects such a broken network, simply output the message "disjoint ". note that the time taken to pass the message from person A to person B is not necessarily the same as the time taken to pass it from B to a, if such transmission is possible at all. Sample Input 32 2 4 3 52 1 2 3 62 1 2 2 253 4 4 2 8 5 31 5 84 1 6 4 10 2 7 5 202 2 5 1 50 Sample output 3 23 10 Source Southern African 2001

Select a starting point from a directed graph to reach all other points from the starting point, and minimize the distance between the starting point and other points.

Idea: first use Floyd to find the distance between all two points, and then enumerate the start point to see if the start point can reach all points and the maximum value is the smallest.

Code:

# Include <iostream> # include <cstdio> # include <cstring> # include <algorithm> # include <cmath> # include <string> # include <map> # include <stack> # include <vector> # include <set> # include <queue> # pragma comment (linker, "/Stack: 102400000,102400000") # define maxn 1005 # define maxn 111 # define mod 1000000009 # define INF 0x3f3f3f # define PI ACOs (-1.0) # define EPS 1e-6typedef long ll; using namespace STD; int MP [Ma XN] [maxn]; int N; void Floyd () // obtain the shortest short circuit between all points {int I, j, k; For (k = 1; k <= N; k ++) for (I = 1; I <= N; I ++) for (j = 1; j <= N; j ++) {if (I = k | j = k) continue; MP [I] [J] = min (MP [I] [J], MP [I] [k] + MP [k] [J]) ;}} int main () {int I, j, M, T, E; while (scanf ("% d", & N) {memset (MP, INF, sizeof (MP); for (I = 1; I <= N; I ++) {scanf ("% d", & M); If (M> 0) {for (j = 1; j <= m; j ++) {scanf ("% d", & E, & T); MP [I] [e] = T ;}} Floyd (); int MI = inf; Int P; int flag = 0; for (I = 1; I <= N; I ++) // enumerate 1 ~ N as the starting point {int MA =-INF; For (j = 1; j <= N; j ++) // determine whether I can be used as the starting point to go from I to all other points if (I! = J) {If (MP [I] [J] = inf) break; MA = max (MA, MP [I] [J]); // find the farthest point starting with I, and record the length} If (j = n + 1) Flag = 1; else continue; If (mi> Ma) // select the minimum maximum time {mi = MA; P = I ;}} if (FLAG) printf ("% d \ n", P, mi ); else printf ("disjoint \ n");} return 0 ;} /* 32 2 4 3 52 1 2 62 1 2 253 4 4 2 8 5 31 5 84 1 6 4 10 2 5 202 2 5 5 1 50 */

Stockbroker grapevine (poj 1125 Floyd + enumeration)